Forms of Bias Flashcards

1
Q

What is Bias?

A

Inclination of scores in a certain (usually favourable) direction, not just random error.

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2
Q

Statistical regression

A

Random component to the severity of symptoms in chronic conditions. Chronic conditions have a cyclical pattern.
Pt’s seek care when symptoms are more severe, more likely next fluctuation will be towards average symptom level.

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3
Q

Placebo effect

A

Improvement in outcomes as a result of treatment ritual

Non-specific treatment effects

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4
Q

Hawthorne effect

A

Changes in behaviour because its known behaviour is under scrutiny. Patients may over or under exaggerate symptoms.

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5
Q

Rosenthal effect

A

Theapist led - high expectation lead to improved performance

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6
Q

Polite patient effect

A

Patient may be reluctant to disappoint therapist and exaggerate recovery when they in fact aren’t feeling better.

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7
Q

Recall bias

A

Therapists more readily remember their successes - extreme cases feature more prominent in memory.

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8
Q

Ways of controlling bias for natural history or statistical regression

A
  • use of comparison group (group that doesn’t get the treatment)
  • groups need to be 100% equivalent
  • randomisation to avoid selection bias
  • subtract the change due to natural history/other treatment
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9
Q

Ways of controlling bias for placebo, Rosenthal and Hawthorne

A
  • sham intervention
  • blind patient: ritual but no Rx
  • blind therapist: don’t know which treatment they are giving (hard to do in physio), the ritual has to be the same
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10
Q

Ways of controlling bias for polite patient effect and detection bias

A
  • independent assessors: removed from clinical process
  • assessors blind to group allocation
  • sometimes the patient is the assessor*
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11
Q

How to control for Selection bias

A
  • comparable groups -> randomisation
  • must have a control group
  • adequate sequence generation
  • concealed randomisation/allocation
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12
Q

How to control for Attrition bias

A
  • keep drop out low (less than 15%)
  • keep group random: state where, when & amount lost
  • sensitivity analysis can help decide if biased
  • use Intention to treat analysis
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13
Q

Definition and How to control for Performance bias

A

participants or therapists desire for a study to fall a certain way

  • blinding of patients (unknown group allocation)
  • blinding of therapists (unaware of treatment allocation - equal enthusiasm)
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14
Q

How to control for Reporting bias

A
  • non-selective report
  • state primary outcomes
  • report primary outcomes appropriately
    • between-group analysis
    • point estimate and variability
    • primary outcomes should relate to the focus of the study
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15
Q

What is spin?

A

Reporting practices that distort the interpretation of results and mislead readers so that results are viewed in a more favorable light.

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